For many years sewing machines have been used to join sheets of fabric together by basically tying the sheets together with thread. Recently, garment manufacturers have started joining sheets of fabric together by welding overlapping edges using heat and pressure. When heat is applied, the overlapping portions of the fabric melt and fuse together forming a seam. This method works well with thermoplastic materials, but less well with woven fabrics. Fabrics are composed of small fibrous materials and when they are heated the fibers become brittle. As a result, the strength and flexibility of the small fibers is compromised. When a tensile force is applied to the seam, the weld is easily broken.
In addition to creating seams using welding techniques, some manufactures have started to join fabric together using adhesive. The basic technique utilizes a strip of adhesive or glue tape, which is positioned between overlapping sheets of fabric. Pressure and heat are then applied to the overlapping fabric and adhesive tape, which generates heat and melts the tape. The adhesive then forms an adhesive bond, joining the overlapping fabric surfaces and, thus, forming an adhesively bonded seam. Although gluing fabric together has been a commercially successful way of manufacturing garments, the completed product exhibits several limitations, depending upon the manner of joining the fabric and the type of fabric used. As illustrated in FIG. 1, if the fabric is joined “face-to-face”, like in a standard sewn seam, the resulting glued seam will separate and fail when a tensile force F of sufficient magnitude is applied to the fabric at an angle to the seam. In the figure, the force F is shown at an angle of approximately 90° to the surface of the seam, which is typical of this type of seam. The seam fails due to the fact that the tensile force F is applied at an angle to the seam, and when the angle is approximately 90°, the force is primarily concentrated at the outside or face end of the seam, causing the seam to separate or peel apart.
Another type of adhesively bonded seam, as illustrated in FIG. 2, is typically formed by overlapping and joining the outside or facing surface of a sheet of fabric to the inside or backing surface of another sheet of fabric. In this instance, the resulting glued seam is stronger because most tensile forces are applied approximately parallel to the seam. However, there are problems with this type of seam. One problem is that the seam has a “raw edge” on the outside or face surface of the garment, and the raw edge easily unravels in normal use. The other problem is that the technique does not work well when the outside or facing surface and the inside or backing surface have different tensile strengths. For example, many modern fabrics have a laminate structure with a waterproof facing fabric, having a high tensile strength, on the outside surface and a knit backing fabric, having a relatively low tensile strength, on the inside surface. When a tensile force F of sufficient magnitude is applied to the fabric at an angle to the seam, or even parallel to the seam, the inner backing fabric is prone to separate from the outer face fabric, and the garment is ruined.
The present invention provides a glued seam and a method of forming a adhesively bonded seam, which overcomes these limitations of conventional seams.